I tried to order a crown for a couple of watches that have the same specs, and what I got was so far off what I wanted, that I'm going to ask for help this time. I have two watches, one with a Cattin C66 movement and one with an EB8800 movement.  They both have the same stem thread and the same crown tube dimensions so I can order two of the same crown.  I spent 40 quid on a fancy Bergeon crown gauge, but it's got thread sizes in mm and not tap sizes.  I don't know how to convert tap sizes